A. FIELD OF THE INVENTION
The present invention relates to a hot melt pressure sensitive adhesive composition and to articles of manufacture incorporating the adhesive composition. The pressure sensitive adhesive of the present invention has the properties of low viscosity and high tensile strength without requiring viscosity adjusters, making it particularly useful for disposable diaper construction and hinge gluing in books. Further, it was discovered that the pressure sensitive adhesive of the present invention also has good high and low temperature performance making it useful for PET bottle labeling or mounting HDPE bases to PET beverage bottles.
B. Prior Art
Hot melt adhesive compositions are known throughout the disposables industry. However, it is equally well-known that a hot melt adhesive composition which is suited for bonding in one application may be completely unsuitable for other applications. For example, disposable diaper construction presents a unique set of problems to the adhesives formulator. The adhesive must possess a high degree of adhesion since it is applied in a series of very narrow lines or dots. Moreover, the adhesive must also possess sufficient adhesive and cohesive strength to provide high tensile strength bonds when subjected to stress so that the laminates used in the construction cannot be easily separated. Additionally, the adhesives must remain flexible and secure with age and not break down in a wet environment. Aesthetically, the adhesive should be white or clear in color.
U.S. Pat. No. 4,526,577 (Schmidt, Jr., et al.) discloses a multi-line construction disposable diaper employing a pressure sensitive hot melt adhesive whose composition requires at least four classes of components. The composition for the Schmidt adhesive comprises a block or multi-block copolymer; tackifying resins having high softening points (about 100.degree.-120.degree. C.); a plasticizing oil; optionally, a petroleum wax; and one or more stabilizers.
Pressure sensitive hot melt adhesive compositions have generally not been suited for performance in the disposable polyethyleneteriphthalic acid (PET) bottle industry, because these adhesive compositions lacked sufficient tensile strength at high and low temperatures. High and low temperature performance is important for maintaining the adherence of labels and the adherence of base cups on beverage bottles where the bottles are subject to repeated cycles of contraction and expansion caused by repeated cycles of refrigeration and room temperature warming.
U.S. Pat. No. 4,212,910 (Taylor et al.) discloses a hot melt adhesive composition suitable for PET bottle assemblies consisting essentially of four classes of components: (1) a block copolymer or a teleblock copolymer; (2) at least one tackifying resin; (3) at least one stabilizer; and (4) at least one wax or oil diluent.